asio 中的io_service::work

Class to inform the io_service when it has work to do.

class work

Member Functions

Name	Description
get_io_service	Get the io_service associated with the work.
io_service	(Deprecated: use get_io_service().) Get the io_service associated with the work.
work	Constructor notifies the io_service that work is starting.
~work	Destructor notifies the io_service that the work is complete.

The work class is used to inform the io_service when work starts and finishes. This ensures that the io_service's run() function will not exit while work is underway, and that it does exit when there is no unfinished work remaining.

The work class is copy-constructible so that it may be used as a data member in a handler class. It is not assignable.

 

有些應用程序希望在沒有pending的消息時，io.run也不退出.

boost::asio::io_service io_service;

boost::asio::io_service::work work(io_service);

Thread()

{

Io_service.run();

}

如果work不被析構，該線程永遠不會退出.在work不被析構得情況下就讓其退出，可以調用io.stop。這將導致 io.run立刻退出，所有未完成的消息都將丟棄。已完成的消息（但尚未進入handler的）也不會調用其handler函數（由於在stop中設置了 stopped_= 1）.

work提供了一個拷貝構造函數，因此可以直接在任意地方使用。對於一個io_service來說，有多少個work實例關 聯，則outstanding_work_就+1了多少次，只有關聯到同一個io_service的work全被析構之后，io.run才會在所有消息處 理結束之后正常退出。